- not stable; not firm or firmly fixed; unsteady.
- liable to fall or sway.
- unsteadfast; inconstant; wavering: unstable convictions.
- marked by emotional instability: an unstable person.
- irregular in movement: an unstable heartbeat.
- noting compounds that readily decompose or change into other compounds.
- lacking stability, fixity, or firmness
- disposed to temperamental, emotional, or psychological variability
- (of a chemical compound) readily decomposing
- physics
- (of an elementary particle) having a very short lifetime
- spontaneously decomposing by nuclear decay; radioactive
- (of an electrical circuit, mechanical body, etc) having a tendency to self-oscillation
